Olefins are traditionally produced from petroleum feedstock by catalytic or steam cracking processes. These cracking processes, especially steam cracking, produce light olefin(s) such as ethylene and/or propylene from a variety of hydrocarbon feedstock. Ethylene and propylene are important commodity petrochemicals useful in many processes for making plastics and other chemical compounds. Ethylene is used to make various polyethylene plastics, and in making other chemicals such as vinyl chloride, ethylene oxide, ethylbenzene and alcohol. Propylene is used to make various polypropylene plastics, and in making other chemicals such as acrylonitrile and propylene oxide.
The petrochemical industry has known for some time that oxygenates, especially alcohols, are convertible into light olefin(s). There are numerous technologies available for producing oxygenates including fermentation or reaction of synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials including coal, recycled plastics, municipal waste or any other organic material. Generally, the production of synthesis gas involves a combustion reaction of natural gas, mostly methane, and an oxygen source into hydrogen, carbon monoxide and/or carbon dioxide. Syngas production processes are well known, and include conventional steam reforming, autothermal reforming or a combination thereof.
Methanol, the preferred oxygenate for light olefin production, is typically synthesized from the catalytic reaction of hydrogen, carbon monoxide and/or carbon dioxide in a methanol reactor in the presence of a heterogeneous catalyst. For example, in one synthesis process methanol is produced using a copper/zinc oxide catalyst in a water-cooled tubular methanol reactor.
The preferred oxygenate to olefin conversion process is generally referred to as a methanol-to-olefin(s) process, where the oxygenate, e.g. methanol, is converted in a reactor to primarily ethylene and/or propylene in the presence of a catalyst—typically a molecular sieve catalyst made from a molecular sieve catalyst composition. The oxygenate to olefin reaction uses a catalyst that is maintained under operating conditions with carbonaceous deposits thereon. The carbonaceous deposits are often referred to as coke. Catalyst, for the purpose herein, is classified according to the size of the catalyst. Catalyst particles are larger than catalyst fines. Catalysts particles are typically retained in the reactor by the particle size separators that disengage or separate the catalyst particles from the effluent stream, which effluent stream passes through the particle size separators into the product recovery train. Catalyst fines are carried into the effluent stream.
Typically catalyst particles above 40 microns are added to the reactor to catalyze a reaction. During the reaction, the catalyst develops carbonaceous deposits. Withdrawing a portion of the catalyst from the reactor and burning the carbonaceous deposits off of the catalyst particles controls the aggregate amount of the carbonaceous deposits on catalyst in the reactor. As the catalyst particles travel through the reactor, they break down into smaller particles due to contact with the various parts of the reactor. As they break down in size, they eventually become catalyst fines. Catalyst fines will have the same overall amount of carbonaceous deposits as catalyst particles. Particle size separators, such as cyclones, are placed in the reactors and regenerators to retain useful catalyst particles in the reactor/regenerator system. Catalyst fines (typically less than 40 microns) are generally not retained by the particle size separators and leave the regenerator through the flue. Catalyst fines in the reactor become carried into the effluent with the product.
The effluent from an oxygenate to olefins reaction comprises a considerable amount of water when compared to other olefin forming processes. This large amount of water and the presence of catalyst with carbonaceous deposits creates unique challenges for effluent clean up and recovery. Catalyst for an oxygenate to olefin reaction is typically a molecular sieve catalyst. It is formed into catalyst particles. The presence of the catalyst fines and large quantities of water make removal and disposal of both the water and catalyst fines a unique problem in the oxygenate to olefin process.
U.S. Pat. No. 6,403,854 describes a two stage quench for use with the oxygenate conversion process. The first stage quench removes catalyst fines. But there is no guidance on how to dispose of the catalyst fines after it is removed from the effluent.
Therefore, it would be desirable to have a process for the disposal and handling of catalyst fines that improves process efficiency. It would also be advantageous to have a catalyst fines handling process that removes carbonaceous deposits from the catalyst before the catalyst fines are disposed.